While amplification of target genomic DNA or cDNA in a library to generate adapter linked DNA that can be copied by RNA polymerases is routinely performed, preparation of synthetic RNA polynucleotides de novo involves a series of reactions which can involve multiple steps and is quite cumbersome. Recently with increasing need to manufacture and study larger RNA polynucleotides including guide RNAs and mRNAs, it is desirable to improve the efficiency of the synthetic methodologies.